1. Field of the Invention
The present invention relates to ceramic igniter devices, and mo-re particularly, to such devices that contain two or more hot zone regions that are electrically connected such as in series or in parallel. These devices are suitably incorporated in a variety of devices, including diesel fuel filters and gas burner apparatus.
2. Background
Ceramic materials have enjoyed great success as igniters in gas-fired furnaces, stoves and clothes dryers. Ceramic igniter production includes constructing an electrical circuit through a ceramic component a portion of which is highly resistive and rises in temperature when electrified by a wire lead. See, for instance, U.S. Pat. Nos. 6,028,292; 5,801,361; 5,405,237; and 5,191,508.
Typical igniters have been generally rectangular-shaped elements with a highly resistive xe2x80x9chot zonexe2x80x9d at the igniter tip with one or more conductive xe2x80x9ccold zonesxe2x80x9d providing to the hot zone from the opposing igniter end. One currently available igniter, the Mini-Igniter(trademark), available from Norton Igniter Products of Milford, N. H., is designed for 12 volt through 120 volt applications and has a composition comprising aluminum nitride (xe2x80x9cAlNxe2x80x9d), molybdenum disilicide (xe2x80x9cMoSi2xe2x80x9d), and silicon carbide (xe2x80x9cSiCxe2x80x9d).
While current ceramic igniters provide good performance for many applications, for at least certain applications the need continues for ceramic igniters with improved properties. For a variety of reasons, ceramic igniters also have not been considered suitable for other applications that nevertheless require a heating or ignition element.
It thus would be desirable to have new ceramic igniters. It also would be desirable to have new ceramic igniters that could be employed in new applications.
We now provide new ceramic igniters that comprise multiple xe2x80x9chotxe2x80x9d or ignition zones. The igniters are useful for a wide range of applications. We have found the igniters of the invention are particularly useful to provide a thermal or ignition element over an extended area. Igniters of the invention are especially useful as an ignition element for fuel traps as well as gaseous fuel burners that have fuel outlets over an extended area.
Preferred igniters of the invention comprise at least two, and suitably three, four, five, six or more hot zones in a single, integral sintered ceramic igniter element. Each hot zone is isolated, e.g. electrically and/or thermally segregated from an adjacent hot zone by an interposed insulative and/or conductive regions. An insulative region has a higher resistivity than the bordering hot zone. Conductive zones provide current to the hot zone regions.
Preferred insulators of the invention comprise one or more, and preferably two, conductive regions that traverse a substantial length of the igniter element. Multiple hot zone regions are disposed throughout the igniter element and communicate with the one or more conductive regions.
The multiple hot zones of a sintered element of the invention are suitably arranged either in series or parallel electrical connection. Application of an electric voltage differential across the igniter device can energize each of the hot zones substantially simultaneously such that each hot zone reaches about the same operational temperature within about the same time to temperature.
We have found that igniters of the invention with multiple hot zones can provide effective heating elements and ignition sources throughout a wide area. In particular, we have found that igniters of the invention can be incorporated into fuel exhaust systems such as diesel traps and provide effective ignition and removal of solids deposited within the trap apparatus. Accordingly, the invention features filters, particularly diesel exhaust filters, that include at least one ceramic multiple igniter element of the present invention.
Igniters of the invention also are particularly useful to provide fuel ignition over an extended area. Specifically preferred is use of an igniter of the invention in a gaseous fuel system where the fuel is dispensed over an extended area, for instance, a gas burner that contains multiple levels of gas outlet ports.
Methods also are provided for preparing ceramic multiple igniter elements and related filters of the invention. Additional methods include igniting material deposited on a filter element, including a diesel trap filter element, using a multiple igniter element of the invention.
Other aspects of the invention are disclosed infra.